Enable PSA by default

LDong-Arm · LDong-Arm · commit cd169a7cf751 · 2021-06-08T14:40:00.000+01:00
To enable Mbed OS PSA on a non-TF-M target, a user only needs to add

    `"target.extra_labels_add": ["MBED_PSA_SRV"]`

without having to touch `"target.features_add"` in `mbed_app.json`.
This slightly simplifies the manual configuration.
diff --git a/getting-started/mbed_app.json b/getting-started/mbed_app.json
@@ -2,7 +2,7 @@
     "target_overrides": {
         "*": {
              "platform.stdio-convert-newlines": true,
-             "target.features_add" : ["EXPERIMENTAL_API"],
+             "target.features_add" : ["EXPERIMENTAL_API", "PSA"],
              "target.components_remove": ["SD"]
         }
     },

Original file line number	Diff line number	Diff line change
`@@ -2,7 +2,7 @@`
`2`	`2`	`"target_overrides": {`
`3`	`3`	`"*": {`
`4`	`4`	`"platform.stdio-convert-newlines": true,`
`5`		`- "target.features_add" : ["EXPERIMENTAL_API"],`
	`5`	`+ "target.features_add" : ["EXPERIMENTAL_API", "PSA"],`
`6`	`6`	`"target.components_remove": ["SD"]`
`7`	`7`	`}`
`8`	`8`	`},`